Third Generation Partnership Project (3GPP) which discusses the specifications for the third generation mobile communication systems provides location registration control of radio terminals.
Upon receiving a communication start request from a user, a radio terminal is connected over a radio link to a radio network controller (RNC) via a radio base station (Node-B). Then, the radio terminal performs authentication and ciphering processing with a core network (CN) device via the Node-B and the RNC, and the radio terminal is connected to the CN device with a radio access line. These behaviors are indicated in FIG. 5 of 3GPP TS 23.251 V7.0.0 (3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Network Sharing; Architecture and functional description (Release 7)).
For example, a serving GPRS support node (SGSN: Serving General packet radio service Support Node) of a CN device performs location management, security management, access control and the like of a radio terminal, and performs location registration by storing subscriber data, such as location information of the radio terminal, in a visitor location register (VLR). However, in a case where the storage amount of the VLR exceeds an allowable range, location registration may not be performed. Thus, the radio terminal may be dealt with as being located in an out-of-service area.
In addition, in order to easily deal with an expected increase in the number of radio terminals, a device for femtocell (hereinafter, described as femto-RNC) that has both the functions of Node-B and RNC and that controls a small number of radio link connections with radio terminals has been introduced. However, in a case where a location registration request is issued from a radio terminal under the control of a femto-RNC, if the above-mentioned storage amount of a VLR in an SGSN that controls the femto-RNC exceeds an allowable range, a situation in which the radio terminal is subjected to out-of-service processing occurs even though the femto-RNC has been installed in order to deal with the expected increase in the number of radio terminals.